Combining a process for conducting a continuous reaction with concurrent separation into a single process technique has received renewed attention in recent years. Various reaction/separation technologies are being investigated and have reached differing degrees of development or commercial viability. Fairly developed techniques include, for example, reactive distillation techniques and reactive chromatography. Other techniques, such as reactive membranes and reactive crystallization techniques, are also being developed. Some of these techniques have provided certain benefits such as reduced capital costs, higher productivity, higher product yields and improved selectivity when competing reactions are taking place. For instance, reactive distillation, where simultaneous reaction and distillation separation processes are carried out, has been implemented for the production of methyl acetate. This technique resulted in five times lower investment and five times lower energy use than the traditional two-step process where the reaction is carried out as a first step and the distillation separation is carried out as a separate second step. Despite these advantages, however, the reactive distillation technique has drawbacks, which include temperature sensitivity and azeotrope formation.
Reactive chromatography systems have also been used for conducting combined reaction and separation. Several different reactive chromatography systems have been investigated including a fixed bed with a pressure swing, cylindrical annular bed with a rotating feed input source, a countercurrent moving bed, and a simulated bed. The choice of a particular reaction/separation technology is made based on the specific requirements of specific applications. Each application will have a particular set of requirements in terms of product yield, purity, process productivity, material handling, etc. (See generally, Vaporciyan, G. G., Kadelec, R. H. AIChE J. 1987, 33 (8), 1334–1343; Fish, B. B.; Carr, R. W. Chem. Eng. Sci. 1989, 44, 1773–1783; and Carr, R. W., In Preparative and Production Scale Chromatography, Ganetsos, G., Barker, P. E., Eds.; Chromatographic Science Series Vol. 61; Marcel Dekker Inc.: New York, 1993; Chapter 18.) Traditionally, the preferred method for carrying out continuous reactive chromatography is the simulated moving bed reactor (“SMB”) configuration.
Traditional SMB technology (as shown in FIG. 1) comprises a circulation flow path having multiple beds packed with solid separation/catalyst filler connected in series to allow a circulation liquid to be forcibly circulated through the beds in one direction. It also has a port for introducing desorbing liquid into the circulation flow path, an extract port for removing circulation liquid carrying the strongly adsorptive constituents (extracts) from the circulation flow path, a feedstock port for introducing feed stock, which contains the constituents to be separated or reacted and separated, into the circulation flow path, and a raffinate port for removing circulation liquid carrying the weakly adsorptive constituents (raffinate) from the circulation flow path.
As shown in the prior art in FIG. 1, the SMB process is illustrated showing a combined reaction and separation by the general reaction A→B+C. The process is illustrated using four “zones.” Typically, although not always, there are two inlets and two outlets in the SMB system unit. The areas defined between them create the four zones. Component A is feed material 11, which is fed into the SMB system between Zone II and Zone III. Component A decomposes to form Component B and Component C. Component B, for example, is the more strongly adsorbed component and therefore moves with the solid in the direction of the extract outlet, which lies between Zone III and Zone IV. At the extract outlet, Component B is collected as extract product 17. Component C is the more weakly adsorbed component and moves with the liquid in the direction of the raffinate outlet, which lies between Zone I and Zone II. At the raffinate outlet, Component C is collected as the raffinate 19 product. The eluent 15 is introduced to the system between Zone I and Zone IV to remove the more strongly adsorbed Component B and to act as the liquid carrier for the system. A number of reactions have been reported:
The SMB process has been demonstrated to increase product yield from equilibrium-limited, liquid phase esterification reactions. Esterification of acetic acid with β-phenethyl alcohol is disclosed in M. Kawase, T. B. Suzuki, K. Inoue, K. Yoshimoto, K. Hashimoto, Chem. Eng. Sci., Vol 51, 2971–2976 (1996). Esterification of acetic acid with ethanol is disclosed in M. Mazzotti, A. Kruglov, B. Neri, D. Gelosa, M. Morbidelli, Chem. Eng. Sci., Vol 51, 1827–1836 (1996); and acetic acid esterification with methanol is disclosed in U.S. Pat. Nos. 5,405,992 and 5,618,972.
U.S. Pat. No. 5,502,248 shows that the equilibrium-limited, liquid phase ester hydrolysis reaction of methyl acetate can be significantly increased through the use of reactive SMB.
Ray A., Tonkovich, A. L., Aris, R., Carr, R. W., Chem. Eng. Sci., Vol. 45, No. 8, 2431–2437 (1990) demonstrates that the product yield from the gas phase equilibrium-limited reaction for hydrogenation of mesitylene can be significantly increased using reactive SMB.
A. V. Kruglov, M. C. Bjorklund, R. W. Carr, Chem. Eng. Sci., Vol 51, 2945–2950 (1996), demonstrates that reactive SMB can be used to increase the product yield with the gas phase reaction for oxidative coupling of methane.
The feasibility of the condensation of phenol with acetone to form bisphenol-A and water and the simultaneous separation of the products has been considered through a numerical simulation (Kawase, M.; Inoue, Y.; Araki, K.; Hashimoto, K. Catalyst Today 1999, 48, 199–209).
Despite these advantages, the traditional SMB techniques have certain drawbacks. The traditional SMB configuration has always been defined as a plurality of beds connected in series and employing a unidirectional fluid flow. The SMB flow pattern also leads to many drawbacks such as high pressure drop, limited flow rate range, difficulty removing strongly adsorbed species, lack of tolerance for solids in the streams and incapability of optimizing conditions for both separation and reaction separately. This limited configuration inherently prevents the system from handling many reaction/separation applications, such as those that require high mass flow, toxin removal, and individual optimization of reaction and separation conditions. With these applications, the traditional SMB reactor system becomes very complicated, very expensive, and sometimes impractical. Furthermore, none of the present technologies allows for a continuous reaction and separation process using contacting beds arranged in parallel, rather than series, having reverse flow capabilities, or combination unit capabilities. Accordingly, it is an object in one embodiment of the invention to provide a process for performing combined reaction and separation that further provides parallel fluid flow, reverse flow, or combination unit design, or a combination of any of these thereby eliminating many of the prior art limitations. It is a further object in an embodiment of the invention to provide a process for performing combined reaction/separation step in a single processing unit to greatly decrease processing cost while increasing throughput.